1. Field of the Invention
The invention is generally related to the area of optical systems and devices. In particular, the invention is related to method and apparatus for combining multiple signals as depolarized output.
2. The Background of Related Art
In optical communication applications, wider spectrums are often used, thus a single light source is not sufficient to cover the entire application demanded spectrum. A typical scenario is the so-called fiber-to-the-home (FTTH) applications where optical signals are needed and defined in a broad spectrum from 1260 nm to 1625 nm range. However, even the super luminescence light-emitting diode (SLED) can only cover <80 nm of spectrum and thus several of them are needed to provide a wide enough spectrum light source.
FIG. 1A shows a prior art approach 100 of combing multiple wavelength spectra light sources (e.g., four wavelengths λ1, λ2, λ3, and λ4 light sources) by using two stages of couplers (also referred to as 2×1 couplers), wherein the first stage of couplers 102 and 104 each combine two light sources, the second stage combines the outputs from the first stage. Because each stage causes 50% loss in power, accordingly, FIG. 1B shows a 6 dB loss in the curve of the combined output 108.
FIG. 2A shows another prior art approach 200 of combing multiple wavelength spectra light sources (e.g., four wavelengths λ1, λ2, λ3, and λ4 light sources) by using two WDM filters 202 and 204 and a coupler 206, wherein two WDM filters 202 and 204 combine λ1, λ2, λ3, and λ4 light sources and output two combined light sources that are coupled together by the coupler 206. As shown in FIG. 2B, the total power loss is around 4 dB as the WDM filters 202 and 204 are typically less than 1 dB in power loss.
It is known in the art that the cost of a WDM filter is a lot more expensive than that of a coupler, but using couplers would introduce more power loss. Furthermore, all these prior arts are limited to providing only one output port and discard or waste other outputs. For many practical manufacturing and other applications where several users need such power light sources, multiple of these devices are needed. Thus there is need for a design that captures all or part of the wasted powers to recycle them for multiple identical output port light source applications, in addition to other benefits and advantages to be appreciated described herein.